Design of silver-zinc-nickel spinel-ferrite mesoporous silica as a powerful and simply separable adsorbent for some textile dye removal

Silver-zinc-nickel spinel ferrite was prepared by the co-precipitation procedure with the precise composition Ag0.1Zn0.4Ni0.5Fe2O4 for bolstering pollutant removal effectiveness while upholding magnetic properties and then coated with a mesoporous silica layer. The surface characteristics and composition of Ag0.1Zn0.4Ni0.5Fe2O4@mSiO2 were confirmed using EDX, FT-IR, VSM, XRD, TEM, SEM, and BET methods. The surface modification of Ag-Zn-Ni ferrite with a silica layer improves the texture properties, where the specific surface area and average pore size of the spinel ferrite rose to 180 m2/g and 3.15 nm, respectively. The prepared spinel ferrite@mSiO2 has been utilized as an efficient adsorbent for eliminating methyl green (MG) and indigo carmine (IC) as models of cationic and anionic dyes from wastewater, respectively. Studying pH, Pzc, adsorbent dosage, dye concentration, and temperature showed that efficient removal of MG was carried out in alkaline media (pH = 12), while the acid medium (pH = 2) was effective for IC removal. Langmuir isotherm and pseudo-second-order kinetics were found to be good fits for the adsorption data. Both dyes were adsorbed in a spontaneous, endothermic process. A possible mechanism for dye removal has been proposed. The adsorbent was effectively recovered and reused.


Adsorption experiments (batch methods)
To assess the adsorption capabilities of the investigated ferrite, a variety of adsorption experiments have been performed.In each experiment, several 100-mL Erlenmeyer flasks were filled with a known amount of adsorbent (5-30 mg) and 25 mL of a dye solution with a known concentration.The containers were placed in a water shaker thermostat and agitated at 120 rpm at a working temperature.After specified intervals of time, the adsorbent was extracted magnetically.The concentrations of MG and IC in the supernatant were determined by measuring the absorbance at 632 nm for MG and 610 nm for IC by using UV-Vis spectrophotometry (Varian Cary 400).The following Eqs.(1-3) were utilized to determine the dye removal percentage and the amount of dye adsorbed at time t (q t ) and at equilibrium (q e ) 48 .where C o is the initial concentration, C t is the concentration at time t, and C e is the concentration of the dyes at equilibrium.The volume of the working solution is denoted by V (L), and the mass of the nanocomposite is m (g).Using universal buffer and either HCl (0.1 M) or NaOH (0.1 M), the pH of the solution was maintained within the desired range (2-12).
where β is the full width at half-maximum for the (311) peak in radians, λ is wavelength, and θ is diffraction angle.The size of the crystallites increased from 5.6 to 10 nm when the Ag + content rose (Table 1).The difference in ionic radii between Ag + (1.26 A°) and Zn 2+ (0.74 A°) may be the cause of this.It was found that the average crystallite size of silica-coated ferrite increased from 5.6 nm for uncoated ferrite to 8.35 nm.This shows that the silica layer was successfully coated.

FTIR
FTIR spectra of prepared metal ferrites are shown in Fig. 4; they span 400-4000 cm −1 .The distinctive band of all metal ferrite Ag x Zn (0.5-x) Ni 0.5 Fe 2 O 4 , where x = (0.1, 0.3, 0.5) , are nearly similar, indicating the same structure of all prepared metal ferrite.There are two prominent absorption peaks observed at 585 cm −1 and 410 cm −1 .These peaks correspond to the vibrational modes of tetrahedral metal-oxygen bonds and octahedral metal-oxygen bonds, respectively 54 .Moreover, when the silver doping ratio is increased, particularly at x = 0.5, both the bands (1)  www.nature.com/scientificreports/related to octahedral and tetrahedral sites display a displacement towards higher wavenumbers.This shift happens due to the replacement of Ag + ions with Zn 2+ ions, which have a higher atomic weight 55 .
The strong band at approximately 3432 cm −1 and the small band at 1638 cm −1 refer to the stretching and bending vibrations of OH groups 56 .The spectrum of Ag 0.1 Zn 0.4 Ni 0.5 Fe 2 O 4 @mSiO 2 (Fig. 4) confirms the presence of the same bands as in mixed ferrite as well as new bands at 1079.54 cm −1 , 965.52 cm −1 , 798.08 cm −1 and 455.8 cm −1 .The stretching Si-O-Si, bending Si-O-Si, streching Si-O, and bending Si-O bands are presented here in the correct order 57 .All these bands indicate that SiO 2 was successfully loaded onto Ag 0.1 Zn 0.4 Ni 0.5 Fe 2 O 4 .

EDX
EDX was used to analyse synthetic samples for elemental makeup (Fig. 5).The atomic percentages of Ag, Zn, and Ni in addition to Fe and O components in prepared samples indicate that spinel ferrite has been successfully prepared.The main elements of the all spinel ferrite Ag x Zn (0.5-x) Ni 0.5 Fe 2 O 4 , where x = (0.1, 0.3, 0.5), were Ag, Zn, Ni, Fe, and O (Fig. 5a and Table 2).In addition to the previously mentioned elements, Si appeared in the spectrum of Ag 0.1 Zn 0.4 Ni 0.5 Fe 2 O 4 @mSiO 2 (Fig. 5b and Table 2), which is largely related to SiO 2 .This reflects the effective loading of silica on the ferrite surface of the composition Ag 0.1 Zn 0.4 Ni 0.5 Fe 2 O 4 .

VSM
At room temperature, VSM confirmed the samples' magnetic characteristics.The magnetic permeability profiles are shown in Fig. 6.All the different compositions of mixed ferrite Ag x Zn (0.5-x) Ni 0.5 Fe 2 O 4 , where x = (0.1, 0.3, 0.5), are superparamagnetic, as evidenced by the presence of a slight hysteresis.In Table 3, the values for saturation magnetization, remanence, and coercivity are recorded.
The saturation magnetization values of mixed ferrite Ag x Zn (0.5-x) Ni 0.5 Fe 2 O 4 , where x = (0.1, 0.3, 0.5), decrease as the ratio of Ag increases, mainly due to the presence of diamagnetic silver components in the Ag-based nanoferrite samples 58,59 .In the case of Ag 0.1 Zn 0.4 Ni 0.5 Fe 2 O 4 @mSiO 2 , the nonmagnetic silica shell is responsible for the drop in saturation magnetization, coercivity, and remanence of Ag 0.1 Zn 0.4 Ni 0.5 Fe 2 O 4 @mSiO 2 60,61 .However, the saturation magnetization of 14.1 emu/g was sufficient for facile separation of Ag 0.1 Zn 0.4 Ni 0.5 Fe 2 O 4 @mSiO 2 from aqueous solutions with a magnet.

SEM and TEM
SEM and TEM techniques were employed to examine the morphological characteristics of the samples.In the SEM image of Ag 0.1 Zn 0.4 Ni 0.5 Fe 2 O 4 @mSiO 2 (Fig. 7a), a smooth surface composed of spherical crystals was observed.TEM images of Ag     morphology of the particles, with an average particle size of approximately 1 µm (Fig. 7b,c).Figure 7c exhibited the successful encapsulation of the ferrite within a thin core-shell structure of silica.Additionally, Fig. 7d displayed the presence of a thin mesoporous silica layer with silica aggregations at various locations on the surface of the ferrite, highlighting its porous nature in HRTEM.

Textural characteristics
The adsorbent surface area is a key factor in raising adsorption efficiency.According to BET and porosity measurements, the specific surface area and pore volume of spinel ferrite were determined to be 69.79 m 2 /g and 0.404 cm 3 /g, respectively.Coating the prepared spinel ferrite with a silica layer increased the specific surface area and pore volume to 180.81 m 2 /g and 0.771 cm 3 /g, respectively.The synthesized materials are porous, as shown by the average pore size (Table 4).According to N 2 -adsorption/desorption isotherm Fig. 8, both the SF and the SFS displayed a type IV with a hysteresis loop of the H 2 (b) type, indicating a mesoporous nature with a wide range of pore size distribution 62 .This takes place in porous materials characterized by a network of interconnected pores as well as in pores characterized by a broad body and a thin neck 63,64 .

Adsorption studies
This research sets out to develop an efficient adsorbent for the elimination of harmful anionic and cationic dyes that pollute water and endanger human health.As a result, the adsorption abilities of different compositions of spinel ferrite Ag x Zn (0.   www.nature.com/scientificreports/ The influence of experimental conditions Significant effects of initial dye concentration, nanocomposite quantity, temperature, and solution pH on the adsorption of various dyes by spinel ferrite@mSiO 2 (SFS) were observed.The results of varying each variable were examined carefully.
Effect of adsorbent dosage.The effectiveness of SFS in eliminating MG and IC was studied by adjusting the dosage from 5 to 30 mg.As illustrated in Fig. 11, the removal percentage for dyes increases as the number of adsorbents increases.This is primarily due to the greater availability of adsorption sites on the adsorbent surface, which allows for more effective interaction between the dye molecules and the adsorption sites [65][66][67] .
The pH effect.The pH level plays a crucial role in influencing the adsorption process.Both adsorbate dyes (MG or IC) and absorbent SFS possess various surface functional groups that gain or lose protons (H + ) in response to the pH of the medium 68 .To optimize the adsorption process for pollutant removal, the adsorption process for MG and IC was examined across the pH range (2-12), as shown in Fig. 12. Pzc measurements show that the point of zero charge (pH pzc ) of SFS is 6.45.At a pH > 6.45, SFS's surface turns negatively charged due to the ionization of H + from the active groups leaving negative charges; as a result, MG removal efficiencies increase with increasing pH above 6.45,where they reached 96.6% at a pH of 10 due to electrostatic interactions between cationic methyl green and negatively charged adsorbents 69 .www.nature.com/scientificreports/However, IC is negatively charged at low pH and has a pKa of 12.6 70,71 .So, the removal efficiencies of IC decrease at pH > 6.45 due to the increased electrostatic repulsion with negatively charged adsorbent surfaces.This result agrees with the work of Yazdi et al. 72 .As a result, the removal efficiency of IC increases with decreasing pH value until it reaches 93.8% at pH = 2 73 (Fig. 12), due to the electrostatic attraction between the cation surface of spinel ferrite and the negative IC, and furthermore, the formation of a hydrogen bond.As a result, the alkaline medium was the right choice for removing methyl green dye, and the acidic medium is efficient for removing IC.
Effect of the initial concentration of dye.The influence of dye concentration on the removal efficiency of pollutant dyes was investigated, as shown in Fig. 13.The removal percentages of MG and IC reached 91% within 90 min below the concentrations of 7 and 19 mg/L for MG and IC, respectively.As the dye concentration increases within 90 min, the percentage of MG and IC that is removed decreases.With an increase in dye concentration, the availability of adsorption sites became restricted, resulting in a decrease in dye removal prior to achieving equilibrium 74 .At higher concentrations, however, the removal effectiveness noticeably drops as a larger number of dye molecules compete for a smaller number of adsorption sites.This decrease is because the previously adsorbed dye molecules are now blocking the active sites of the remaining molecules in solution 75 .

Kinetics of adsorption
The time-dependent behaviour of adsorption is depicted by the linear and non-linear adsorption kinetics of the pseudo-first and second-order models in, Eqs. ( 5)-( 8) 76 .For the water treatment to be successful and economical, the adsorption process must be completed quickly.The contact time is the duration of time it takes for the maximum amount of dye adsorbed to reach equilibrium with the adsorbent surface in an adsorption  experiment.Figure 14 shows how the quantity of MG and IC adsorbed (q t ) varies with contact time in a nonlinear kinetic model.After 110 min of interaction, the q t had climbed to an equilibrium level.Also, the mechanism of adsorption of MG or IC dyes onto synthesized ferrite is determined by evaluating the adsorption kinetics in the intra-particle diffusion model, Eq. ( 9) 77 .
(5) ln q e − q t = lnq e − k 1 t (6)  www.nature.com/scientificreports/Adsorbed dye amounts are given in terms of mg/g at equilibrium (q e ) and contact time (q t ) in minutes.Pseudo-first order diffusion has a rate constant of k 1 (min −1 ), pseudo-second order diffusion has a rate constant of k 2 (g/mg min), and intra-particle diffusion has a rate constant of k i (mg/g min 1/2 ).The values of the correlation coefficient (R 2 ) in Table 5, indicate that the linear and nonlinear equations forms of the pseudo-second-order approach, Eqs.(7, 8), respectively, are a better fit and more suited for the experimental data than the linear and nonlinear pseudo-first-order model Eqs.(5, 6), respectively.Also, for each dye under examination, the q e, exp , and the q e estimated from the pseudo-second-order model are all quite close to one another, within the experimental errors.Adsorption kinetics may be altered by a number of different processes.Most constrained are the processes of diffusion, which can only occur via (a) extracellular diffusion, (b) boundary layer diffusion, and (c) intra-particle diffusion 77,78 .Therefore, an intra-particle diffusion kinetic model is used to further evaluate the adsorption data and forecast the rate-limiting stage in the process.If the qt vs. t 0.5 linear plot is through the origin, then intra-particle diffusion is supposed to be in charge of the adsorption process, as predicted by this theory.Figure 15 shows that q t is linearly related to t 0.5 .Here we see examples of both the outer and inner surface diffusions; the former refers to the surface's exterior while the latter describes its interior.According to Table 6, there is a completely quick step of diffusion from the outside onto the adsorbent surface, followed by a completely sluggish step of diffusion into the inner surface 75 .

Adsorption isotherm models
The surface properties, maximum capacity of the adsorbent, and adsorption mechanism were all stated by the values of certain parameters determined from adsorption isotherm models used to examine the produced ferrite's (9) q t = k i t 1/2 + C  www.nature.com/scientificreports/potency and capacity as an adsorbent.Different adsorption isotherm models were employed to compare the results; these included the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) models.Figure 16 shows nonlinear adsorption isotherm of MG and IC on SFS as a compared with SF adsorbent.Adsorption of dye molecules onto an adsorbent surface has the same activation energy according to the Langmuir isotherm, as shown in Fig. 16, which assumes monolayer adsorption above a homogenous adsorbent surface with a set number of identical sites 79 .This led to the adsorption data of MG and IC being fitted into the nonlinear form of Langmuir's equation 80 , the determination and quantification of the maximum adsorption capacity (q max ) were performed and tabulated in Table 7.
where C e is the concentration of dye at equilibrium in mg/l, q e is the adsorption capacity of dye at equilibrium in mg/g, q max is the maximum possible adsorption capacity in mg/g, and K L is the Langmuir constant in L/mg.
Table 7 shows the results.Adsorption results agreed with the Langmuir model, which postulated the existence of homogenous adsorption sites on SFS substrate, as indicated by high values of the correlation coefficient (R 2 ) for the isotherm plots.The IC dye has sulfonated, amine, and hydroxyl groups in its structure that support electrostatic binding with mesoporous silicate Si-OH through hydrogen bonds, which may explain why the IC dye has a higher Langmuir monolayer coverage capacity value (q max ) than the MG dye and why the value of the same dye increases when using SFS as an absorbent.The results show that ultimate capacity q max and K L values increased as the temperature of adsorption increased, thus, the affinity of the adsorbent to the investigated dyes increased with increasing temperature.
The maximum monolayer adsorption capacity (q max ) for methyl green and indigo carmine adsorption is compared across a variety of adsorbent surfaces in Table 8.We found that our SFS as an adsorbent is effective in removing methyl green and indigo carmine from aqueous solutions, when compared to data from the relevant literature.
An experimental expression that accounts for surface heterogeneity and an exponential distribution of site and energy energies is the Freundlich isotherm 81 .The Freundlich adsorption Eq. ( 11) describes this equilibrium.
The Freundlich isotherm constant is denoted by k F ((mg/g) (mg/L) −1/n F ) 82 , where n is the dimensionless exponent of the Freundlich.K F and n are the determined values.Estimates of n F in this work ranged from 4 to 7, ( 10)    www.nature.com/scientificreports/indicating that the adsorption processes are close to irreversible 83 .When the K F value is large, the adsorption is driven with greater efficiency.This means that the adsorption driving force for IC dye is greater than that for MG dye, and the driving force grows when SFS is employed as the adsorbent.The favourable nature of the adsorption process is confirmed at higher temperatures by an increase in K F value 84 .Adsorption data for MG and IC were analyzed using the Temkin isotherm model.This model supports limited interactions between the adsorbent and adsorbate and demonstrates that all molecules in the surface layer have decreased adsorption energies at the cover surface.Additionally, it was believed that adsorbate-adsorbent interactions directly reduced the adsorption heat with coverage 85 .Equation (12) represents the Temkin isotherm model.
where K T (L/mol) represents the equilibrium binding constant, R is the perfect gas constant, T is the absolute temperature, and b (kJ/mol) represents the heat of adsorption.Table 7's b values match up with an adsorption mechanism involving electrostatic interactions and hydrogen bond formation.Temperature has a beneficial influence on the binding energy of dyes with ferrite surfaces, as evidenced by the rise in K T as the temperature rises.
To identify the adsorption mechanism (physical or chemical), we can use Dubinin-Radushkevich isotherm Eqs.(13-15) to determine the activation energy E (KJ/mol).Adsorption has been explained by ion exchange adsorption if E ranges from 8 to 16 kJ/mol; if E is 8, the process has been validated physically.Adsorption in this study may occur by chemisorption or ion exchange, where E ranges from 8 to 16 kJ/mol.where q s (mol/kg) is the theoretical capacity of adsorption calculated from Eq. ( 13) of the D-R model, ε (kJ/mol) is the Polanyi potential, and β (mol 2 /kJ 2 ) is the mean free energy of adsorption for each molecule adsorbed as given by Eq. ( 14).

Thermodynamics studies
The Langmuir model is the best-fitted model at the different temperatures according to the R 2 values in Table 7.The effect of temperature on the adsorption process according to the Langmuir isotherm is studied as shown in Fig. 17, where q max and K L (L/mg) at different temperatures are shown in Table 9.To determine the thermodynamic parameters, the obtained equilibrium constant must become dimensionless before being applied to the Vant´Hoff equation using Eq.16 95 .
where γ is the activity coefficient (dimensionless) and [Dye]° is the standard concentration of dye (1 mol/L).
The entropy ΔS° and enthalpy ΔH° of adsorption are determined according to the Eqs.(17, 18) from the intercept and slope of the relationship between lnK 0 e vs. 1000/T, respectively, where R is the perfect gas constant (8.314J/mol K), and T is the absolute temperature 96 .The adsorption of MG or IC dye onto the synthesized ferrite is endothermic due to the positive values of ΔH° as shown in Table 9.Also, the measured ΔH° values varied from 25 to 48 kJ/mol, suggesting that both physisorption and chemisorption may be involved in the adsorption of the dyes of interest 97 .Adsorption is characterized by an increase in the degree of disorder at the solid-solution interface, as measured by an increase in the entropy parameter, ΔS°9 8 .This is the normal outcome of electrostatic force interactions that lead to the phenomenon known as physical adsorption.The spontaneous process for MG and IC sorption is revealed by negative values of ΔG°, and as the temperature is raised, the value of ΔG° decreases even further, showing that the adsorption process is more favoured at a higher temperature 99 .
Characterization Silica coated spinel ferrite after Adsorption.FTIR analysis.A Comparison of the FTIR spectra of the used SFS before and after adsorption of IC as a model of the investigated dye showed the appearance of additional peaks after their contact with the IC dye (Fig. 18).Peaks appearing at 2930 cm were due to CH stretching, at 1374 cm −1 , it corresponds to the C-H bending vibration or C-N stretching vibration of amines 100 .A comparison between newly appeared peaks and those of IC  www.nature.com/scientificreports/showed that the new peaks were probably the characteristic of this textile pollutant.The band broadening about 3400 cm −1 is assigned to the vibration formed by hydrogen-bonded -O-H groups in the absorbent and adsorbate molecules.The band broadening at 3390, 3433 cm −1 indicate to the hydrogen bonding in comparison to the FTIR analysis before the adsorption process as well as existence of (-NH) stretching bond of dye 101 .
The N-H bond between the dye's N atom and the H-O-H bond resulted in a noticeable shift of the H-O-H peak from 1638 to 1627 and an increase in its width.This effect resulted from the establishment of oxygenhydrogen bonds between the dye and the adsorbent 102 .The adsorption of molecules onto the SFS nanoparticles in this study is consistent with physical adsorption mechanisms, involving hydrogen bonding and electrostatic forces.The low adsorption heat indicated by the Temkin isotherm model, the formation of a monomolecular layer according to the Langmuir isotherm, and FTIR analysis collectively support the physical adsorption process on the SFS nanoparticle surface.SEM/EDX analysis.Scanning electron microscopy revealed a substantial change in surface shape following adsorption (Fig. 19).SEM-EDX analysis was used to analyse the morphological aspects of SFS.The dye molecules appear on the surface of spinel ferrite.The principal components of ferrite/IC are Fe, Ni, Zn, O, Si, and C, N from dyes, according to the EDX analysis, confirming the efficient adsorption of IC.

Reusability and recovery study
The regeneration and reusability of adsorbent surfaces are critical aspects of determining their true value.The use of adsorbents with high adsorption capacity and high desorption assets reduces additional environmental pollution and overall costs.As a result, desorption studies on SFS are carried out to determine its recyclable accessibility.The adsorbent was recovered by treating the used sample with 0.1 M HCl for 2 h, washing it three times with distilled water, and finally testing the filtrate with a silver nitrate solution to make sure the HCl was  www.nature.com/scientificreports/gone before drying it at 45 °C for 18 h.For four cycles, 20 mg of adsorbent was used.The elimination percentage changed with each cycle, as seen in Fig. 20 103 .

The proposed mechanism of adsorption
Based on the provided information and the characteristics of the adsorption process, here is a suggested mechanism for the adsorption of MG and IC dyes onto the synthesized ferrite material.From pH and PZC studies, when the pH level goes above 6.45, active groups ionize and make the surface of the synthesised SFS material negatively charged.This negative charge makes it easier for the positively charged cationic methyl green (MG) dye molecules to stick to the negatively charged surface of the adsorbent.This electrostatic interaction is a dominant driving force for MG adsorption.On the other hand, indigo carmine (IC) dye is negatively charged at low pH.The IC dye contains sulfonated, amine, and hydroxyl groups in its structure.These functional groups can form hydrogen bonds with the mesoporous silicate (Si-OH) on the adsorbent surface.The presence of hydrogen bonding sites enhances the adsorption of IC dye onto the adsorbent.All these were confirmed by Temkin, Freundlich, and Dubinin-Radushkevich.It is thought that an increase in temperature gives more thermal energy, which helps both MG and IC dyes stick to the adsorbent surface because the adsorption process is endothermic.This increased energy facilitates the interactions between the dye molecules and the adsorbent.The positive values of ΔH°, which range from 25 to 48 kJ/mol, suggest that MG and IC dyes may bind by both physisorption and chemisorption mechanisms, using hydrogen bonds and electrostatic interactions.The second order and

Figure 1 .
Figure 1.Structure of the investigated dyes.

Figure 2 .
Figure 2. Illustrative steps for the synthesis of SFS.
5-x) Ni 0.5 Fe 2 O 4 , where x = 0.1, 0.3, and 0.5, to remove MG and IC from simulated wastewater were studied and compared.It was found that Ag 0.1 Zn 0.4 Ni 0.5 Fe 2 O 4 (SF) is more efficient in dye removal, as shown in Fig. 9. Therefore, Ag 0.1 Zn 0.4 Ni 0.5 Fe 2 O 4 was chosen for more adsorption studies, especially because it has the highest saturation magnetization for easy separation.Subsequently, the coating of the chosen spinel ferrite (x = 0.1) with a silica layer increased in surface area from 69.79 to 180.08 m 2 /g, as proven by BET.As shown in Fig. 10, the absorbance of MG and IC dyes diminishes over time after adsorption by SFS.

Figure 7 .
Figure 7. SEM image of SFS (a) and TEM images of SF (b) and SFS (c,d).

Figure 9 .
Figure 9.The comparison of the removal efficiency of MG (4 mg/L) and IC (19 mg/L) utilising 20 mg of various adsorbents Ag x Zn( 0.5−x) Ni 0.5 Fe 2 O 4 at pH = 7 and 25 °C.

Figure 11 .
Figure 11.Removal efficiencies of MG (13 mg/L) and IC (37 mg/L) using SFS as a function of adsorbent dosage.

Figure 12 .
Figure12.The removal efficiency of MG (13 mg/L) and IC (37 mg/L) utilizing SFS as a function of medium pH molecules are now blocking the active sites of the remaining molecules in solution75 .

Figure 14 .
Figure 14.Non-linear kinetic model for adsorption of MG (a) and IC (b) on SFS.

Figure 15 .
Figure 15.Intra-particle diffusion kinetics model of the of MG and IC on SFS.

Figure 16 .
Figure 16.Nonlinear adsorption isotherm of MG (a,b) and IC (c,d) on SF and SFS, respectively.

Figure 17 .
Figure 17.Nonlinear Langmuir adsorption isotherm of MG (a,b) and IC (c,d) on SF and SFS, respectively at different temperatures.

Figure 18 .
Figure 18.FTIR of SFS before (a) and after adsorption (b) of IC.

Figure 19 .
Figure 19.SEM/EDX of SFS after adsorption of IC.

Figure 20 .
Figure 20.The reuse of dyed SFS samples.

Figure 21 .
Figure 21.Proposed mechanism of the adsorption of MG and IC dyes on SFS.

Table 2 .
The atomic percentage of various samples.

Table 5 .
Kinetics data of the linear and non-linear forms of adsorption of methyl green and indigo carmine on SF and SFS.

Table 6 .
Adsorption of MG and IC dyes onto SF and SFS through intra-particle diffusion.

Table 7 .
Adsorption isotherms parameters of methyl green and indigo carmine dye at 25°C.

Table 8 .
Maximum adsorption capacity (q max ) comparison of MG and IC on various adsorbents.

Table 9 .
Adsorption process thermodynamic characteristics for both MG and IC at various temperatures.